In achieving fully integrated wireless communication systems, an antenna switch is utilized to change modes (e.g., transmit and receive modes) or frequency bands (e.g., high and low bands). In performing these tasks, the insertion loss of the antenna switch should be minimized to guarantee a high efficiency of the transmitter as well as a low noise figure of the receiver. The antenna switch should also isolate the receiver from the transmitter effectively during respective receive and transmit modes, and vice versa. In addition, high power signal from the transmitter should be handled without significant distortions by the antenna switch to preserve the linearity of transmitters.
The power handling capability of an antenna switch depends primarily on the voltage swing over the OFF-state receiver switches of the antenna switch. A large signal from the transmitter induces the unwanted channel formation and forward biases junction diodes of the OFF-state receiver switch devices. Also, this can cause a device breakdown, which results in linearity degradation of the transmitter. Because transmitted signals from a power amplifier can have large voltage swing (e.g., more than 1 W based upon peak-to-peak 20V at 50Ω load) in the case of cellurar applications, reducing the voltage swing over the OFF-state receiver switches is important to enhance the power handling capability of the antenna switches.
The efficiency of a power amplifier is one of the most dominant factors in determining the whole transmitter performance. Particularly, output matching network of the power amplifier takes a critical portion of it. Since the output impedance of the power amplifier is usually small enough to generate a high power signal, the output matching network of the power amplifier is forced to have a large impedance transformation ratio to match the output impedance to the antenna. As the impedance transformation ratio increases, the efficiency of the matching network is typically degraded.